EP3199972A1 - Systems and methods for protecting against high-radiant-flux light based on time-of-flight - Google Patents

Systems and methods for protecting against high-radiant-flux light based on time-of-flight Download PDF

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Publication number
EP3199972A1
EP3199972A1 EP16204968.8A EP16204968A EP3199972A1 EP 3199972 A1 EP3199972 A1 EP 3199972A1 EP 16204968 A EP16204968 A EP 16204968A EP 3199972 A1 EP3199972 A1 EP 3199972A1
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EP
European Patent Office
Prior art keywords
shutter
light
mirror
optical path
imaging device
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP16204968.8A
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German (de)
English (en)
French (fr)
Inventor
Brian J. TILLOTSON
Kathryn M. NEVILLE
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Boeing Co
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Boeing Co
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Filing date
Publication date
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Publication of EP3199972A1 publication Critical patent/EP3199972A1/en
Pending legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/70—Circuitry for compensating brightness variation in the scene
    • H04N23/73—Circuitry for compensating brightness variation in the scene by influencing the exposure time
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/4804—Auxiliary means for detecting or identifying lidar signals or the like, e.g. laser illuminators
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/495—Counter-measures or counter-counter-measures using electronic or electro-optical means
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/02—Catoptric systems, e.g. image erecting and reversing system
    • G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B17/00—Systems with reflecting surfaces, with or without refracting elements
    • G02B17/02—Catoptric systems, e.g. image erecting and reversing system
    • G02B17/06—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror
    • G02B17/0605—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using two curved mirrors
    • G02B17/061—Catoptric systems, e.g. image erecting and reversing system using mirrors only, i.e. having only one curved mirror using two curved mirrors on-axis systems with at least one of the mirrors having a central aperture
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/02—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices involving prisms or mirrors
    • G02B23/08—Periscopes
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/12—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices with means for image conversion or intensification
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
    • G02B26/02—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the intensity of light
    • G02B26/04—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the intensity of light by periodically varying the intensity of light, e.g. using choppers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/50—Constructional details
    • H04N23/55—Optical parts specially adapted for electronic image sensors; Mounting thereof
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/02—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices involving prisms or mirrors
    • G02B23/06—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices involving prisms or mirrors having a focussing action, e.g. parabolic mirror
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G02B5/10—Mirrors with curved faces
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/52—Optical limiters

Definitions

  • This invention generally relates to systems and methods for the protection of imaging devices against light having a high radiant flux.
  • high-radiant-flux light means light having any one or more of the following measurable properties: high radial intensity (W/sr), high irradiance (W/m 2 ) and high radiance (W ⁇ sr -1 ⁇ m -2 ).
  • Such high-radiant-flux light may be coherent (e.g., laser light) or incoherent..
  • a general problem is to achieve high probability of mission success, at acceptably low cost, despite hazards.
  • a hazard of increasing concern is high-radiant-flux light, which can damage optical sensors (hereinafter “image sensors”) needed to (a) operate a vehicle safely or (b) collect data, such as agricultural data or military surveillance data.
  • image sensors optical sensors
  • This hazard usually arises from lasers aimed at a vehicle. However, it may also arise from arc welding equipment, exceptionally large or hot fires, a lightning bolt, or a nuclear blast.
  • Imaging devices such as cameras and telescopes, are especially vulnerable to high-radiant-flux light.
  • imaging devices use a lens or mirror to focus light onto an image sensor (such as a focal plane array) comprising a multiplicity of pixels. This greatly increases the light intensity on pixels corresponding to the location of the high-radiant-flux light source in the image.
  • image sensor such as a focal plane array
  • the high-radiant-flux light can damage the image sensor by thermal shock, melting, or other mechanisms.
  • the term "laser sensor” means a sensor that detects high-radiant flux light (defined above). (For avoidance of doubt, it should be noted that the term “laser sensor” as used herein does not mean a sensor that detects laser light only or a sensor that detects all laser light. Instead the laser sensor detects any light having a radiant flux in excess of a specified threshold, including but not limited to high-radiant-flux laser light.)
  • the laser sensor transmits a signal via a signal line to a shutter inside the imaging device. The shutter closes, blocking the light from reaching the image sensor of the imaging device. This approach suffices for the weakest threats, such as accidental exposure to lasers used in a light show, but it is insufficient for the more intense light commonly encountered in military situations due to reaction time delays in such a system.
  • the present invention is directed to systems and methods for preventing high-radiant-flux light, such as laser light or a nuclear flash, from causing harm to imaging devices, such as a camera or telescope.
  • high-radiant-flux light such as laser light or a nuclear flash
  • the proposed systems share the common feature that a shutter is closed sufficiently fast that light from the source will be blocked from reaching the focal plane of the imaging device.
  • Most of the proposed systems include a folded optical path to increase the allowable reaction time for closing the shutter.
  • an imaging device comprising: a laser sensor configured to output an activation signal in response to impingement thereon of light having a radiant flux greater than a specified threshold; an image sensor comprising a multiplicity of elements that convert impinging light to electrical signals; a first path-bending optical component disposed along an optical path that extends from a point in a vicinity of the laser sensor to the image sensor; a first shutter disposed along a portion of the optical path that extends from the first path-bending optical component to the image sensor; and a signal line connected to carry the activation signal from the laser sensor to the first shutter.
  • the laser sensor, the signal line and the first shutter can be configured so that in response to some light and other light, both having a radiant flux greater than the specified threshold, concurrently arriving at the laser sensor and a starting point of the optical path respectively, the first shutter will become opaque prior to the other light impinging thereon in response to receipt of the activation signal from the laser sensor via the signal line.
  • the optical path is configured to produce a time-of-flight delay for light traveling from the vicinity of the laser sensor to the first shutter, and the laser sensor, the signal line, and the first shutter are configured to produce a shutter delay from the time a high-radiant-flux arrives at the laser sensor to the time the first shutter becomes opaque, wherein the time-of-flight delay is greater than the shutter delay.
  • the imaging device may further comprise a second shutter disposed along a portion of the optical path that extends from the first path-bending optical component to the first shutter.
  • the first shutter comprises an electro-optical shutter and the second shutter comprises a mechanical shutter.
  • the invention also related to an instrument comprising: a laser sensor configured to output an activation signal in response to impingement thereon of light having a radiant flux greater than a specified threshold; a first path-bending optical component disposed along an optical path that extends from a point in a vicinity of the laser sensor to a focal plane of the instrument; a shutter disposed along a portion of the optical path that extends from the first path-bending optical component to the focal plane; and a signal line connected to carry the activation signal from the laser sensor to the shutter.
  • the instrument may further comprise second, third and fourth path-bending optical components, wherein the second path-bending optical component is disposed along a portion of the optical path that extends from the first path-bending optical component to the focal plane, the third path-bending optical component is disposed along a portion of the optical path that extends from the second path-bending optical component to the focal plane, and the fourth path-bending optical component is disposed along a portion of the optical path that extends from the third path-bending optical component to the focal plane.
  • the invention also relates to an imaging device comprising: a laser sensor configured to output an activation signal in response to impingement thereon of light having a radiant flux greater than a specified threshold; an image sensor comprising a multiplicity of elements that convert impinging light to electrical signals; means for increasing a time-of-flight of light along an optical path that extends from a point in a vicinity of the laser sensor to the image sensor; a shutter disposed along a portion of the optical path that extends from the volume of substance having a high index of refraction to the image sensor; and a signal line connected to carry the activation signal from the laser sensor to the first shutter.
  • the structure that performs the function of increasing a time-of-flight of light along an optical path comprises a volume of substance having a high index of refraction. In other embodiments, the structure that performs the function of increasing a time-of-flight of light along an optical path comprise one or more reflective surfaces.
  • the invention also relates to a method comprising: (a) detecting a radiant flux entering an optical instrument that has above a specified threshold; (b) when the specified threshold is reached or exceeded, sending an activation signal via a signal line to a shutter disposed inside the optical instrument; (c) delaying the arrival of the entering light at a shutter inside the optical instrument by an amount of time equal to a time-of-flight delay; and (d) in response to sending of the activation signal, the shutter becomes opaque at a time which is subsequent to a time when step (a) occurs by a total shutter delay, wherein the time-of-flight delay is greater than the total shutter delay.
  • FIG. 1 depicts an imaging device 10a that has a lens 12, an image sensor 14, and a housing 16.
  • the housing 16 has an aperture through which incident light propagates on its way to the focal plane of the imaging device 10a.
  • the arrows in FIG. 1 indicate optical paths 18 of respective incoming light rays 18 that are being focused by the lens 12 onto a portion of the image sensor 14, thereby increasing the light's intensity. (Other light rays are not shown to avoid clutter in the drawing.) This greatly increases the intensity on pixels corresponding to the location of the high-radiant-flux light source in the image. Thus, light that is harmless to a structural surface may have damaging intensity at the image sensor 14.
  • FIG. 2 shows an imaging device 10b that has a lens 12, an image sensor 14, a laser sensor 20, and a shutter 22, all of which components may be attached directly or indirectly (by support means not shown) to a housing 16.
  • the laser sensor 20 detects the presence of high-radiant-flux light in the imaging device's field of view.
  • the laser sensor 20 transmits an activation signal via a signal line 24 to the shutter 22 when high-radiant-flux light is detected.
  • the shutter 22 becomes opaque, thereby blocking at least some of the incoming light from reaching the image sensor 14 disposed at the focal plane of the imaging device 10b.
  • the approach depicted in FIG. 2 may be insufficient for blocking the intense light commonly encountered in military situations.
  • the reason for this insufficiency lies in the following three delays: (1) the laser sensor response time ⁇ t sensor (any laser sensor requires a non-zero time to detect the arrival of high-radiant-flux light and send a signal); (2) the signal transit time ⁇ t transit (the signal must travel from the laser sensor 20 to the shutter 22; it cannot travel faster than the speed of light, 0.3 meter per nanosecond); and (3) the shutter response time ⁇ t response (no shutter can close instantly; it requires a nonzero reaction time to become opaque after a signal arrives; the shorter the reaction time, the more costly the shutter).
  • These delays can be summed to produce a single value ⁇ t shutter , which is the total shutter delay from when high-radiant-flux light arrives at the laser sensor 20 to when the shutter 22 becomes opaque.
  • FIG. 3A is a graph of light intensity at an image sensor versus time for two laser attacks of differing intensities I 1 and I 2 .
  • FIG. 3B is a graph of temperature at the same image sensor versus time for the same laser attacks.
  • the plot labeled I 1 in FIG. 3A represents a relatively low-intensity attack beginning at time t 0 .
  • the plot labeled T 1 ( t ) in FIG. 3B represents the corresponding temperature at the focal plane. Starting at t 0 , the temperature rises from an initial value T 0 toward the damage threshold T damage . Before it reaches that threshold, the shutter 22 closes at time t cl ose . The temperature stops rising, and the image sensor 14 survives.
  • the plot labeled I 2 in FIG. 3A represents a higher-intensity attack.
  • the plot labeled T 2 ( t ) in FIG. 3B represents the corresponding temperature at the focal plane.
  • the temperature rises from the initial value T 0 , but given the higher intensity I 2 , the temperature rises faster than in the weak attack.
  • the temperature exceeds the damage threshold T damage before the shutter 22 closes at t close . In this event, the image sensor 14 may be damaged or destroyed.
  • the protection systems described in detail below can block even the highest-intensity light before it damages the focal plane.
  • FIG. 4 depicts structural and functional aspects of an imaging device 10c equipped with a protection system in accordance the present invention.
  • the imaging device 10c comprises the following elements: a lens 12 (or other image-forming optics), an image sensor 14 (or other image sensor); a mirror 28 (or other path-bending optic(s); a laser sensor 20; a shutter 22 (electro-optical, mechanical, etc.); a signal line 24 (a wire, coaxial cable, or optical fiber); a housing 16a having an aperture; and a baffle 26.
  • the mirror 28 reflects light from the lens 12 onto the image sensor 14.
  • the optical path length from a point near the laser sensor 20 to the shutter 22 via the mirror 28 is much longer than the length of the signal line 24 from the laser sensor 20 to the shutter 22.
  • the elongated housing 16a surrounds and protects the components and the optical path.
  • Baffle 26 blocks any light scattered by diffraction, dust or other blemishes on lens 12 from reaching shutter 22 via any path with an optical path length less than the optical path length from a point near the laser sensor 20 to the shutter 22 via the mirror 28
  • FIG. 4 depicts the process for protecting the imaging device 10c from incoming high-radiant-flux light includes the following major steps:
  • the optical path length ⁇ s is long enough to impose a time-of-flight delay ⁇ s / c , where c is the speed of light, and this time-of-flight delay is greater than the total shutter delay ⁇ t shutter . That is, ⁇ s / c > ⁇ t shutter
  • the image sensor 14 may comprise a staring focal plane array that includes a multiplicity of elements that convert impinging light to electrical signals, such as a charge coupled device (CCD) sensitive to visible or infrared wavelengths.
  • CCD charge coupled device
  • it can be a single-pixel camera (compressive imaging system), an imaging photomultiplier, a vidicon tube, a photochemical film, or others.
  • the image-forming optics may comprise a lens, a mirror, or a combination thereof that focuses light on the image sensor to create an image. It may be a single optical element such as the lens 12 shown in FIG. 4 , or a multi-element system such as an achromatic lens, a Newtonian mirror system, or a Schmidt-Cassegrain lens-mirror combination.
  • the path-bending optics may comprise an optical element, such as a mirror 28, that changes the direction of light.
  • the direction is changed by at least 90°. This includes light that forms the image and light that can damage the image sensor. Changing the light's direction allows the path length of the light to be much greater than the path length for the shutter signal.
  • this optical element may be a reflecting prism, multiple mirrors, or combinations thereof. The mirror can be curved and is part of the image-forming optics.
  • the laser sensor is a photosensitive electronic device that has roughly the same field of view as the imaging device. When a sufficiently high-radiant-flux light appears in its field of view, the laser sensor transmits a signal quickly-typically in less than a nanosecond. As seen in FIG. 4 , preferably the laser sensor 20 is positioned near the shutter 22 so the signal line 24 from the laser sensor 20 to the shutter 22 will be short. The laser sensor 20 is typically much less sensitive than the image sensor 14, as it only needs to respond to high-radiant-flux light. It can also survive exposure to light having a higher radiant energy than what the image sensor 14 can be exposed to.
  • a typical laser sensor comprises a processor having a thresholding function, a photodetector, and a lens or other focusing element to provide directionality.
  • the shutter 22 is a device that has two states. In one state, the shutter 22 at least partially blocks the passage of light. In the other state, the shutter 22 allows the passage of light.
  • the shutter 22 may comprise crossed polarizers surrounding a fast-acting magneto-optical or electro-optical device such as a Pockels cell, a Kerr cell, a Faraday modulator, or an active-matrix liquid-crystal grid (similar to the technology used in liquid crystal displays). To give the shutter 22 as much time as possible to receive the activation signal and to respond, the shutter 22 is typically adjacent to the image sensor 14 and as close as possible to the laser sensor 20.
  • the signal line 24 carries a signal from the laser sensor 20 to the shutter 22.
  • the signal line 24 is configured to take as direct a route as possible from laser sensor 20 to shutter 22.
  • the signal line 24 may be optical fiber (signal speed ⁇ 2 x 10 8 m/s), or it may be a free-space path (perhaps shielded by a hollow tube) along which the signal moves at 3 x 10 8 m/s.
  • the signal line 24 is configured to have minimal inductance and capacitance per unit length to achieve the highest possible signal speed.
  • the housing 16a shown in FIG. 4 could be designed to achieve a two-meter path in one meter of length by positioning the mirror 28 one meter from each of the laser sensor 20 and the shutter 22.
  • a mechanical shutter is too slow to act before the high-radiant-flux light reaches the image sensor, but once closed, it blocks 100% of the light.
  • Affordable electro-optical shutters typically do not block 100% of the light, so some alternative embodiments use both types of shutters in tandem: the electro-optical shutter acts quickly to block most of the light, and the mechanical shutter subsequently blocks the rest of light.
  • FIG. 5 also depicts structural and functional aspects of an imaging device 10d equipped with a protection system in accordance with the present invention.
  • the protection system comprises a slower mechanical shutter 22a "upstream" from a faster electro-optical shutter 22b.
  • the mechanical shutter 22a is tougher (i.e., more rugged) than the electro-optical shutter 22b, so as shown in FIG. 5 , the mechanical shutter 22a is positioned to protect the weaker, more costly electro-optical shutter 22b from prolonged exposure to high-radiant-flux light.
  • FIG. 6 shows how adding a mechanical shutter 22a helps protect the image sensor 14.
  • the signal line from the laser sensor 20 to the mechanical shutter 22a is not shown to avoid clutter in the drawing.
  • the electro-optical shutter 22b closes at time t close_1 , but since it does not block 100% of the light, the temperature of the image sensor 14 (or other image sensor) continues to rise slowly.
  • the mechanical shutter 22a closes at time t close_2 , which is later than the time t close_1 when the electro-optical shutter 22b closed.
  • the closed mechanical shutter blocks 100% of light, so that the temperature at the image sensor 14 (or other image sensor) rises no further (i.e., does not reach the temperature T damage at which damage might occur).
  • a Cassegrain reflector is a combination of a concave primary mirror 30 and a convex secondary mirror 32, often used in optical telescopes.
  • both mirrors are aligned about the optical axis, and the primary mirror 30 usually contains a hole in the centre, thus permitting the light to reach an eyepiece, a camera, or a light detector.
  • FIG. 7 depicts structural and functional aspects of a Cassegrain imaging device 10e (e.g., a telescope having a Cassegrain reflector) equipped with a protection system having a shutter 22 near the secondary mirror 32.
  • FIG. 7 shows use of the Cassegrain primary mirror 30 as both a path-bending optical element and an image-forming optical element.
  • the incoming light rays travel by respective long optical paths through the housing 16b.
  • a first portion 18a of respective optical paths for two light rays extends from a point in the vicinity of the laser sensor 20 to the primary mirror 30;
  • a second portion 18b of the respective optical paths for the two light rays extends from the primary mirror 30 to the secondary mirror 32;
  • a third portion 18c of the respective optical paths for the two light rays extends from the secondary mirror 32 to the image sensor 14.
  • a benefit of the invention as depicted in FIG. 7 is that light passes through the shutter 22 twice on its way to the image sensor 14. This increases the effective opacity of the shutter 22: a shutter 22 that blocks 90% of the light in a single pass blocks 99% of the light in a double pass. This allows an inexpensive shutter to work as well as a more expensive one.
  • FIG. 8 depicts an alternative that avoids this.
  • a Cassegrain imaging device 10f is equipped with a protection system having a shutter 22 disposed behind the primary mirror 30 and in front of the image sensor 14. Placing the shutter 22 behind the primary mirror 30 puts the extra shutter hardware out of the optical path. In some applications, this may be preferable despite losing the double-pass advantage provided by the embodiment depicted in FIG. 7 .
  • FIG. 9 depicts structural and functional aspects of a Newtonian imaging device 10g (e.g., a Newtonian telescope) equipped with a protection system having a shutter 22 near the laser sensor 20.
  • a Newtonian imaging device 10g e.g., a Newtonian telescope
  • a protection system having a shutter 22 near the laser sensor 20.
  • Incoming light is reflected and focused by a concave primary mirror 30 onto a flat diagonal secondary mirror 32a the latter in turn reflects the focused beam onto the image sensor 14.
  • This optical configuration places the shutter 22 behind an aperture in the housing 16c and very close to the laser sensor 20 and keeps the extra shutter hardware out of the optical path.
  • FIG. 10 depicts structural and functional aspects of an imaging device 10h equipped with a protection system having a shutter 22 in which multiple path-bending optics create a very long optical path.
  • the imaging device 10h comprises the following elements: a lens 12, an image sensor 14, mirrors 28a and 28b, a laser sensor 20, a shutter 22, a signal line 24, a housing 16d having an aperture, and a pair of baffles 26a and 26b.
  • the first mirror 28a reflects light from the lens 12 onto the mirror 28b; the mirror 28b reflects light from mirror 28a back onto mirror 28a; and the mirror 28a reflects light from mirror 28b toward the shutter 22.
  • the optical path length from a point near the laser sensor 20 to the shutter 22 is much longer than the length of the signal line 24 from the laser sensor 20 to the shutter 22. More specifically, the incoming laser light travels by a long optical path through the housing 16d. A first portion 18a of that optical path (indicated by a first arrow in FIG.
  • a fourth portion 18d of that optical path extends from the mirror 28a to the shutter 22.
  • the imaging device has one or two major bends in the optical path.
  • the invention uses multiple path-bending optics to create very long optical paths in limited physical space.
  • the version shown here keeps the optical path roughly in a single plane and has non-crossing legs in the optical paths.
  • the device's volume can also be minimized by having optical path legs that cross, e.g., in a star pattern or a three-dimensional mesh.
  • Multiple reflecting surfaces can introduce substantial optical errors, so some embodiments use adaptive optics between the shutter and the image sensor to correct any errors.
  • the apparatus included a folded optical path.
  • Another way to delay the arrival of high-radiant-flux light at an image sensor is to use a substance having a high index of refraction to delay the time-of-flight.
  • FIG. 11 also depicts structural and functional aspects of an imaging device 10i in accordance with the present invention.
  • a portion of the optical path 18 can be filled with a transparent substance 34 (solid, liquid, or gas) that has a high index of refraction n. That is, the speed of light in the material is slowed by a factor of, say, 1.33 (water) to as much as 4.0 (germanium, used in long-wave infrared imagers) or higher (exotic substances such as Bose-Einstein condensate).
  • the optical path is effectively lengthened by the high-index substance 34 disposed inside the housing 16e. Signals propagating along the signal line 24 are not slowed, so they can travel as fast as the speed of light in vacuum.
  • the activation signal reaches the shutter 22 well in advance of the high-radiant-flux light.
  • the shutter 22 becomes opaque (i.e., closes) before the light reaches it whenever the following relation is true: n ⁇ s / c > ⁇ t shutter
  • the optical path may comprise multiple legs, each leg i having length ⁇ s i and index of refraction n i .
  • the appropriate relation is: ⁇ n i ⁇ s i / c > ⁇ t shutter where ⁇ denotes a sum over all legs.
  • the invention can use both a folded optical path and a path that is at least partially filled with a high-index substance.
  • a path-bending element is a prism
  • the refractive index of the prism is at least 1.3, so light traveling through it incurs a substantial delay.
  • the prism can be prism designed to have a large internal path length and to incorporate material with unusually high index of refraction.
  • the invention can have a shutter between the image-forming optics and the image sensor.
  • the image-forming optics may be between the shutter and the image sensor (i.e., "downstream” of the shutter). The path-bending optics and the laser sensor would remain "upstream” of the shutter.
  • FIG. 12 is a diagram depicting structural and functional aspects of a periscope 8 equipped with a protection system having a shutter 22 placed in front of the eye of a human observer 6 and further having an extended optical path. The extended optical path through the periscope 8 allows shutter 22 to close before high-radiant-flux light reaches the eye of the human observer 6.
  • the regular periscope structure is extended below the viewer's eye to increase the optical path. (Other parts of the periscope optics are omitted for clarity.) This longer path allows the signal from the laser sensor 20 to reach the shutter 22 before the high-radiant-flux light reaches the shutter 22. A first portion 18a of that optical path (indicated by a first arrow in FIG.
  • a second portion 18b of that optical path extends from the mirror 36 to a first facet of a prism 38; a third portion 18c of that optical path (indicated by a third arrow) extends from the first facet of prism 38 to a second facet of prism 38; and finally a fourth portion 18d of that optical path (indicated by a fourth arrow) extends from the mirror 28a to the shutter 22.
  • the forward opening of the periscope can be at the same height as the human observer, whereby the point is not necessarily to see over an obstacle, but rather simply to protect the observer's eyes from high-radiant-flux laser light or other high-radiant-flux light.
  • the activation threshold may be based on radiant intensity (e.g., watts per steradian), irradiance (e.g., watts per square meter), or radiance (e.g., watts per steradian per square meter).
  • radiant intensity e.g., watts per steradian
  • irradiance e.g., watts per square meter
  • radiance e.g., watts per steradian per square meter.
  • Slightly different laser sensors can be employed depending on whether radiance or irradiance is being detected.
  • the laser sensor may comprise a single photodetector.
  • the laser sensor should comprise a focusing element, a photosensitive chip with multiple pixels, and a processor that issues the activation signal when the amount of light on one pixel exceeds the threshold.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Astronomy & Astrophysics (AREA)
  • Remote Sensing (AREA)
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  • Spectroscopy & Molecular Physics (AREA)
  • Studio Devices (AREA)
  • Telescopes (AREA)
  • Blocking Light For Cameras (AREA)
  • Camera Bodies And Camera Details Or Accessories (AREA)
  • Optical Radar Systems And Details Thereof (AREA)
  • Image Input (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
EP16204968.8A 2016-02-01 2016-12-19 Systems and methods for protecting against high-radiant-flux light based on time-of-flight Pending EP3199972A1 (en)

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US10605984B2 (en) 2016-12-01 2020-03-31 Waymo Llc Array of waveguide diffusers for light detection using an aperture
US10502618B2 (en) 2016-12-03 2019-12-10 Waymo Llc Waveguide diffuser for light detection using an aperture
JP6484272B2 (ja) * 2017-03-17 2019-03-13 株式会社フジクラ レーザ加工装置およびレーザ加工方法
US10698088B2 (en) 2017-08-01 2020-06-30 Waymo Llc LIDAR receiver using a waveguide and an aperture
CN109387845A (zh) * 2017-08-07 2019-02-26 信泰光学(深圳)有限公司 测距模块
US10890650B2 (en) 2017-09-05 2021-01-12 Waymo Llc LIDAR with co-aligned transmit and receive paths
KR102582961B1 (ko) * 2018-03-28 2023-09-26 삼성전자주식회사 디스플레이를 보호하는 웨어러블 장치 및 그 방법
CN110727114A (zh) * 2019-10-31 2020-01-24 歌尔股份有限公司 一种头戴式显示设备
CN112067126A (zh) * 2020-08-17 2020-12-11 中国科学院国家空间科学中心 一种用于大气探测的星载极紫外高光谱相机光学系统
RU2749872C1 (ru) * 2020-10-13 2021-06-17 Федеральное государственное казенное военное образовательное учреждение высшего образования "Военный учебно-научный центр Военно-воздушных сил "Военно-воздушная академия имени профессора Н.Е. Жуковского и Ю.А. Гагарина" (г. Воронеж) Министерства обороны Российской Федерации Способ защиты оптико-электронного средства от воздействия мощного импульсного лазерного излучения

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AU2016256791A1 (en) 2017-08-17
BR102016028610B1 (pt) 2022-12-06
JP2017138578A (ja) 2017-08-10
JP6981747B2 (ja) 2021-12-17
AU2016256791B2 (en) 2021-03-04
CA2949267C (en) 2022-05-31
CA2949267A1 (en) 2017-08-01
BR102016028610A2 (pt) 2017-08-08
CN107026984B (zh) 2021-01-26
US9948866B2 (en) 2018-04-17
CN107026984A (zh) 2017-08-08

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